Circuit interrupter



July 1l, 1933. a. P. BAKER Er Al.

CIRCUIT INTERRUPTER Filed July 26, 1932 3 Sheets-Sheet l U f 2 5 7 A? 2 9 2 //ll\\ nu., 7 J i 1 Q N V. lil h Z ...n l Tull. a /f xl/, -L 4 Il 7% //l\\ L llll 1w WI /Mf f ,./IHIIII l n Q s f @J J. `1l Jl# f L L Z fw 4J .J 5f

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ATTOR Y July 11, l1933.

B. P. BAKER E-r AL 1,918,232`

CIRCUIT INTERRUPTER Filed July 26, 1932 3 Sheets-Sheet 2 July 11,1933. B. P. BAKER n ,L 1,918,232

CIRCUIT INTERRUPTER Filed July 26, 1932 3 Sheets-Sheet 3 BY /Q ATTORN Y Patented `luly ll, 1933 UNITED STATES PATENT OFFICE BENJAMIN P. BAKER, OF TURTLE CREEK, PENNSYLVANIA1 AND MAURICE W. BRAINARD',

OF LOS ANGELES, CALIFORNIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC AND MANU- FACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CIRCIT INTERRUPTER Application filed July 26,

Our invention relates to circuit breakers and particularly to circuit breakers of the type in which the breaker operating means is manually operable to open or to close the circuit, and is automatically operable to open the. circuit and to prevent the holding of the circuit closed upon the occurrence of short circuit or overload conditions.

One object. of our invention is to provide an improved multi-pole circuit breaker of this type which shall be more economical to manufacture, and which shall be lnore reliable in operation, than the breakers heretofore known in the art.

Another object of our invention is to provide means for a. multi-pole circuit breaker, having a single operating mechanism which engages the center pole, whereby the normal pressure between the engaging contact members may be augmented, particularly on the outer poles, through the action of a force substantially proportional to the magnitude of current flowing in the breaker.

Another object of our invention is to provide an improved switch member assemblage for circuit breakers of this type which shall have magnetic means associated therewith for preventing the displacement of any one of the switch members by the magnetic forces set up during the occurrence of an overload or short circuit. condition in the controlled circuit.

A further object of our invention is to provide a magnetic means for preventing the chattering of circuit breaker contacts during the occurrence of heavy overload conditions.

A still further object of our invention is to provide an improved circuit breaker switch member having a pivoted contact member, and magnetic means for biasing the pivoted contact member to the closed position.

In electrical apparatus. whenever the axis of a current-carrying conductor deviates from a straight line, niagnetic forces are set up which tend to further distort the curved portion of the cur-rent-carr ving conductor. It is ver)- diilicult to design a circuit breaker of the type herein disclosed in which the current-carrying path through the engaging contacts maintains a straight line relation- 1932. Serial No. 624,758.

ralit y of poles; allof the switch members bcing mechanically tied together by a tiebar. In a multi-pole circuit interrupter using a single operating mechanism and having contact members whose engaging contact faces are not normal to the axis of the path of current flow, this tendency of the contacts to disengage, as a result of the magnetic forces set up, during overload conditions, is eX- tremely disadvantageous and undesirable.

One solution of the problem is to make the ticbar and switch member frames of sufficient rigidity that the magnetic forces may be. entirely counterbalanced thereby. This, however, is not an economical nor a satisfactory solution because it makes for very cumbersome and expensive parts, and greatly in. creases the design difficulties involved.

lVith our invention, however, we have provided a magnetic means whereby' a force directly proportional to the magnitude of the current flowing in the interrupter is supplied to counterbalance the force tending to separate the engaging contact faces.v Furthermore. our invention vpermits the application of this counterbalancing force at the point where it is most effective, that is, at a pointA adjacent to the point at which the undesired force originates.

The principal field for immediate application of our invention is in connection with circuit breakers for controlling lighting and distribution feeder circuits, and we shall hereinafter describe an embodiment of our invention as applied t0 such circuit breakers, without.however, in any way intending-to restrict the scope of our invention, except as indicated in the appended claims.Y

In this embodiment of our invention, we

nism;

provide a plurality of switch members and a plurality of stationary contact members having engaging cont-act faces for opening a plurality of poles. In addition, we provide a manually operable mechanism for opening and closing the breaker contacts with a snap action, leaf springs for biasing the engaging Contact faces toward each other with a predetermined normal force, an insulating base on which the structure is assembled, an arc-extinguishing device foreach pole, coil springs for biasing each of the switch members to the open position, a releasable restraining mean-..1 for holding all of the switch members closed, a. unitary, removable tripping device for releasing the restraining means in response to a predetermined electrical condition in any one pole, thereby opening all -of the poles of the breaker, and magnetic means for supplying an additional force biasing the engaging contact faces toward each other.

'llie features of our invention which we bclieve to be new are particularly pointed out in the appended claims, and for a full under- 25 standing of the principles of the invention reference may be had to the accompanying drawings, in which,

Figure 1 is a plan view of a three-pole cir- /cuit breaker embodying the principal elements ofour invention; the cover has been cut away to show part of the breaker mecha- Fig. 2 is a sectional view on theline II-H of Fig. 1; certain of the parts are shown in elevation to more clearly illustrate the structural features involved Fig. 3 is a fragmentary perspective view of the assembly of switch members; the base has been eut away to more clearly show the structural featuresinvolved, and

Fig. 4 is a fragmentary sectional view on the line IV -IV of Fig. 3. v

Referring to the drawings, the base 1 is of molded insulating material and has mounted thereon the terminal contacts 3 and 5tlie unitary trip' structure 7, the circuit breaker operating mechanism 9 which has associated therewith the assemblage of the switch members 11, and the arc extinguishers 13 which have integral therewith the main stationary contacts 15 and the'auxiliary stationary contacts 17. .A switch member 11 and statioiary contact-s 15 and 17 are provided for each of the three polos. Each of the poles is insulatad from the adjacent pole by one of the insulating barriers 19,-whicii iin, molded in um base 1. These insulating barriers 19 align with similar barriers (not shown) in the cover 21, which is likewise of molded material7 and thereby effectively prevent flashovers between adjacent poles during the in-' terruption of heavy current arcs.v

The operating handle 23'. which is rigidly affixed tothe switch operating mechanism 9, is of molded insulating material, and it has vsingle operating mechanism.

a portion 25 which extends through a suitable opening 27 in the cover 21. The unitary trip structure 7 has a base 29, of insulating material, and a removable cover A31, also of insulating material. The unitary trip structure 7 fits in a suitable recess in the insulating base 1 and is fastened therein, as will be described later, through the agency of suitable screw fastenings.

The electrical circuit for each of the poles is substantially the same. Beginning with the terminal contact 3, the current passes suc- Y cessively through the arc extinguishing structure 13, the stationary contact 15, the moving contact member 32 and the conducting shunt 33 associated with the switch member 11, the unitary trip structure 7each of the shunts 33 connecting with one of the termi nals 35 of the trip device-aiid thence throughL the trip structure to the other terminal contact 5.

Each of the switch members 11 has a channel shaped 4frame 37, of iron, upon which the remainder of the structure is assembled. T he moving contact 32 is pivotally fastened to the iron frame 37 by the pivot pin 39 which extends through two holes placed in opposite sides of the frame 37. Two cotter pins 41 prevent the pivot pin 39 from moving out of position. One end of the flexible shunt 33 is fastened to the moving contact 32 by the rivets 43, and the other end is provided with a terminal portion 45 for engaging the corresponding terminal 35 of the trip structure 7 the screws 47, which engage suitable threaded recesses 49 in the base 1, being provided to releasably connect those terminals.

Each of the moving contact members 32 has an end portion 49 extending into the frame 37 (Fig. 4). This end portion 49 is engaged by the free end of two fiat steel springs 51 and 53'; the other end of both of the springs being rigidly fastened to the frame 37 by rivets 55.

A square tie bar 57, of insulating material, extends across all three poles of the breaker, and is rigidly'afiixed to one end of each of the switch members 11 (Figs. 3 and 4) by means of iron straps 59, which loop about the bar 57 and have projections 60 (Fig. 4) which extend through suitable openings in 4 the'frame 37 and are therein clinched. This bar 57 serves as a tiel means for rigidly connecting together all of the switch members 11, and thereby making it possible to operate all three of the switch members from a mechanism 9 engages the frame 37 of the central switch member 11; the two other switchmembers 11 are operatively connected to thc mechanism 9 by the tie bar 57. Thus, all of the switch members 11 are moved simultaneously, either to open' or close thebreaker contacts in response to a movement of tht operating handle 23, or to open the breaker contacts in response to an overload or short circuit condition in the circuit controlled by'any one of the poles.

Each of the channel shaped iron frames 37 has two portions '61, which extend outwardly from the sidesI of the frame. 'l`hese portions 61 are positioned beneath the pivot pin 39, which supports the coiltact member 32, and are adapted to be attracted to a U-shaped iron member 63 embedded in the insulating base 1. A flat headed screw 65 is provided for more securely fastening the members 63 to the base 1. When the interrupter is in the fully closed position, an air gap 67 (Fig. 4) exists between the projections 61 and the cooperating member 63. This air gap makes it possible for the member 63 to attract the frame 37 of each of the outer switch members 11 when energized by the magnetic flux due to the current flowing through the breaker.

The attracting force is substantially proportional to the magnitude of the current, and is of great value in maintaining the normal pressure,between the engaging contact faces of the moving contact 32 and the stationary contact 15. The attractive force between the frame 37 and the member 63 is not directly transmitted to the engaging faces of the contact members, but is made effective through the action of the springs 51 and 53; that is, the contact member 32 is biased clockwise. (Fig. 4) about its pivot 39 by this magnetic attraction, and movement in this direction is opposed by the springs 51 and 53, and by the magnetic action of the flexible shunt to be described later.

The facing 68 of the main stationary contact 15 and the engaging portionA 69 of the moving contact member 32 are composed of silver in order to improve the current-carrying qualities. The facing 70 of the auxiliary stationary contact 17 and its engaging portion 71 are composed of an arc resisting alloy of tungsten and silver; the proportions being 60% of the former and 40% of the latter. )Ve prefer to use arc resisting material for i these contact surfaces in order to reduce to a minilnum the injurious citects of the are which is established therebetween during the operation of the breaker.

The are extinguishers 13 which we prefer lo usewith our invention are of the spacedplate type. in .which a plurality of composite plates, each having a portion of magnetic material and a. central portion of non-magnetic material are provided. Each composite pate is insulated from the adjoining plate and has a slot therein. The extinguishers are disposed adjacent to the arc path, the slots being of substantially the same outline as the moving contacts, and upon the establishment of the arc, due to thek altering of the magnetic field adjacent to the arc path, force the are to move into the spaces between the plates where it is rotated by suitable means associated with the extinguisher until it is extinguished.

The details of construction and the principles of operation of this type of arc extinguisher are completely described in the application of M. W. Brainard, Serial No. 593,236, which was tiled February 16, 1932, and which is also assigned to the assignee of this application.

The operating mechanism 9, some of the details of which are more fully described in Patent 1,786,796, issued December 30, 1930 on an application filed by F. G. Von Horn and assigned to the assignee of this application, comprises in general, a U-shap'ed base 73, a pair of toggle linksl 75 and 77 for engaging the assemblage of the switch members 11, a trigger 79 for releasably restraining the toggle links 75 and 77 in an operative position, a bifurcated operating lever 81, and springs 83 for connecting the operating lever 81 to the knee of the toggle links and the operating handle 23. The U-shaped base 73 is axed to the insulating base 1 of the circuit breaker proper by means of four screws 85, and,` in addition, it has a downwardly projectlng portion 87 (Fig. 2) which is engaged by the central screw 47. A pivot pin 89 extends through suitable aligned openings in the U- shaped base 73, and engages the frame 37 of the central switch member 11. This pin 89 provides a pivot point for the assemblage of switch members 11, all of which are mechanically tied together by the tie bar 57.

Other holes are provided in the U-shaped base 73 for the reception of the pivot pins 91-one on either side of the U-which provide pivot points for the bifurcat'ed operating lever 81. One end of the toggle link 75 is pivotally connected to the frame 37 of the central switch member 11 by the pin93. The pin 93 serves to connect the operating mechanism 9 with the assemblage of switch members. The other end of the toggle link 75 is pivoted to one end of the second toggle link 77 by means of the knee pivot pin 95. The knee pivot pin 95 has means associated therewith for engaging one end of each of the operating springs 83, one on either side; the other end of the operating springs 83 is connected to the bifurcated operating lever 81, and through it to the operating handle 23.

The trigger 79 which is pivoted about the pin 97 provides a releasable restraining means for holding the toggle links 75 and 77 in thel operative position; the movement of the trigger 79 in a counter-clockwise direction (Fig. 2) about the pin 97 is limited by the projections 99, which extendsl inwardly from both sides of the U-shaped base 73. The other end of the toggle link 77 is pivotally fastened to the trigger 79 by the pin 101.

-The movement of the bifurcated operating member 81 is limited by the inwardly extending projections 99 and 103 of the U-shaped base. The projecting end 125 of the trigger 79 is releasably engaged by the latch 107 associated with the trip structure. As previously pointed out, the trip structurev7 is a unitary device entirely assembled upon its own insulating base 29 and completely removable from the breaker; the screws 47 and Jthe bolts 109 with their associated nuts 111 being utilized to lnount the trip structure on the base land to make the necessary electrical connections. `The trip structure 7 includes a thermally responsive element and a mechanically responsive element for each of the three poles.

The details of construction and the operation of the trip device which weprefer to use with our invention are completely described in the application of Harry J. Lingal, Serial No. 600,624, which was tiled March 23, 1932, and which is also assigned to the assignee of this application.

The trip latch 1.07, which engages the end of trigger 79, is slidably pivoted about a pin 113 which extends through suitable openings in two brackets 115, which are ahxed to the trip base 29 by rivets 117. The free end 119 of the latch 107`projects through a suitable opening in the trip base 29 for engaging the mechanism therein. The latch 107 has two slots 121 for slidably engaging the pivot pin 113. A spring 123 exerts a force which prevents the slots 121 from disengaging the pivot pin 113, and, in addition, the spring 123 biases the latch 107 in a counter-clockwise direction (Fig. 2). The movement of the; latch in a counter-clockwise direction is limited by the projection 124, which extends inwardlyv from onel of the bracket arms 115. When trigger 79 is in the operative position, that is, when the end 125 is engaged by the latch 107, the latch is biased in a clockwise direction due to the relatively large force transmitted by the trigger. This force is balanced by the trip mechanism which engages the free end 119.01? the latch 107 and prevents it from turning under the biasing action of the trigger 79.

The shunt 33, which is used in each of the switch members 11, is formed from a plurality of thin laminations substantially rectangular in shape. These laminations are joined together at one end to form the contact portion 45, and are similarly fastened together at the other end 46 in order that' the shunt may be connected to the moving contact member 32. Due to the laminated construction of the body portion of the shunt 33, a comparatively large amount of flexibility is secured. As shown in Fig. 4, the breaker is in the closed position and is not carrying current. The dotted outline of the shunt 33 in Fig. 4 shows the position taken by the shunt when current is flowing through the interrupter. The movement of the body of the shunt into the frame 37 and against the springs 51 and 53 is a result of the distortion of the magnetic field about the current-carrying shunt, the channel shaped frame being of iron, a magnetic material.

The inward moving shunt presses against the springs 51 and 53, and the end 49 of the contact member 32, and biases that member counter-clockwise about its pivot pin 39 (Fig. 4). This biasing action tends to increase the contact pressure between the engaging contact faces 68 and 69, and also facilitates the shifting of the current-carrying path from the main contacts to the auxiliary contacts during the opening of the interrupter.

The biasing action of the shunt 33 is par-v ticularly eli'ective when combined with the previously described magnetic means for attracting the frame 37 of the two outer Contact members 11 to the base 1, because the attraction between each of these frames 37 and its cooperating member 63 holds that frame in a substantially fixed position during all conditions of load and permits the biasing force of the shunt to be transmitted directly to the en aging contacts. It should be noted at this polnt that the entire assemblage of the switch members 11 is pivoted on the pin 89 which engages the central switch member. Thus, the two outer switch members 11 are held in position only by lthe force transmitted through the tie bar 57-the operating mechanism 9 being aiixed to the central switch member-and if some means were not provided for holding the frame 37 of each of the two outer switch members 11 in a fixed position, the magnetic forces set up during overload conditions would cause those frames to move upwardly-due to torsional yielding of the tie bar v57and the attraction of the shunt 33 would result in vlittle or no increase in contact pressure. It isnot necessary to provide supplementary means for holding the frame central switch member because the operating mechanism is directly connected to the frame of that member.

Referring particularly to Fig. 2, wherein the circuit breaker of our invention is shown in the closed position, it will be noted that the center of the toggle links 75 and 77 has moved to an over-center locked position. Thus the contacts 15 and 32 are held against each other with a substantially uniform contact pressure movement of the central switch member 11 is transmitted to the switch members for the outer poles by the tie bar 57, as has been previously pointed out. The opening process i'.- substantially the reverse of the closing process, the knee of the toggle being moved, in this case, upwardly.

The combination of the toggle mechanism and the operating springs connected at the knee thereof makes it possible to open and close the breaker contacts with a snap action. The proportions of the moving contacts 82 are such that the circuit controlled by each pole is first made and finally interrupted through the auxiliary stationary contact 17 and the tip 71 of the engaging moving contact 252. When the breaker is in the fully closed position, the auxiliary stationary coi:- tact 17 does not engage the moving contact 32.

When the breaker is in the closed position and an overload comes on the circuit controlled by any one of the poles, the trip devicel 7 acts to release the free end 119 of the latch 107, and permits the trigger 79 to rotate counter-clockwise (Fig. 2) about the pivot pin 97. One end of the toggle link 77 is carried above the center line of the toggle and the toggle then collapses downwardly, thereby opening the breaker.

Should an attempt be made to close the breaker against an overload or against a short circuit condition, the latch 107 will be released by the trip mechanism 7 immediately after the contacts are closed. The trigger 79 will likewise be released and will cause the toggle mechanism to break so as to open the breaker independently of the position of the' operating handle. Thus, it is not possible to hold the breaker closed against a short circuit or against a continued overload.

When the breaker has been opened by the trip device, it is necessary to restore the mechanism to the operative position. The projection 127 on the operating handle 23 is provided for this purpose. Following the tripping of the breaker, the handle 25 may be moved downwardly (Fig. 2), whereupon the projection 127 will engage the end 105 of the trigger 79, and the progressive downward movement of the handle 23 will cause the trigger to rotate clockwise about its pivot 97. As the operating handle 23 nears the downward limit of travel, the end 125 of the trigger abuts against the overhanging portion 129 of the latch 107- the trigger 79 having been returned by its biasing spring 123 to its normal latched position where it is held by the trip mechanism-and moves the entire latch (Fig. 2) toward the base 29, the latch sliding in the slots 121. Finally, the projecting endr125 of the trigger 79 passes beneath the overhanging portion 129 of the latch 107, and the latch snaps back to the normal position under the inliuence of its biasing spring 123. The entire breaker mechanism is now in the open operative position and may be closed by a movement of the operating handle 23 exactly as described above.

Our invention is particularly effective in maintaining the normal contact pressure between the engaging contact faces during overload conditions. When the interupter is carrying normal current, the inherent rigidity of the tie bar 57 and the frame members is usually sufficient to maintain the normal contact pressure between the engaging contact faces. As the current in the interrupter increases, however, the magnetic force biasing the engaging contact faces apart becomes progressively greater. But, the magnetic force holding the frames in the normal position, and the magnetic force biasing the moving contact into the engaged position are also increasing. Thus, it may be seen that our invention provides a means for maintaining the normal contact pressure between the engaging contact faces of multi-pole circuit interrupters regardless of the load condition on the circuit.

vVhile in accordance with the patent statutes we have given the foregoing details of a practical embodiment of our invention, it is to be understood that many of these are merely illustrative, and that variations oi' their precise form will be desirable in sonic application. )Ve desire, therefore, that the language of the accompanying claims be accorded the broadest reasonable construction, and that our invention be limited only by what is explicitly stated in the claims and by the prior art.

We claim as our invention:

1. In a circuit interrupter, a stationary Contact member, a movable switch member cooperating therewith for opening and closing the circuit, said movable switch member including a conducting member and a pivotally mounted contact member for engaging said stationary contact member, and magnetic means for biasing said engaging contact members toward each other, said magnetic biasing means including a member of magnetic material positioned adjacent said conducting member.

2. In a circuit interrupter, separable contact members, having engaging contact faces, for opening and closing the circuit, supporting means for each of said Contact members, and magnetic means for biasing said contact faces toward each other, one of said separable contact members being pivotally fastened to said supporting means'and having a conducting member afiixed thereto, said magnetic biasing means including a member of magnetic material for attracting said conducting member.

3. A switch member for acircuit interrupter, including a frame member having a portion of magnetic material, a contact member pivotally mounted on said frame member, and a conducting member aiixed to said pivotally mounted contact member, said conducting member having a portion extending along the portion of magnetic material of said frame member and being attracted thereto.

4. In a circuit interrupter, a fixed contact member, and a movable switch member cooperating therewith for opening and closing the circuit, said switch member including a rame member having a portion of magnetic material, a contact member pivotally mounted on said frame member, spring means for biasing said pivotally mounted Contact member toward said fixed contact, and a conducting shunt fastened to said pivotally mounted contact member, saidshunt having a portion extending along said portion of magnetic material and being magnetically attracted thereto, the attraction of said shunt and said magnetic portion biasing said pivotally mounted contact member toward said lixed contact member.

5. In a circuit interrupter, a stationary contact member, and a switch member cooperating therewith for opening and closing the circuit, said switch member including a substantially channel shaped frame of magnetic material, a contact member pivotally mounted on said frame, and a conducting shunt affixed to said pivotally mounted contact member, said conducting shunt having a portion extending through a portion of said channel shaped frame, and being magnetically attracted thereto, said attraction biasing said pivotally mounted contact member toward said stationary contact.

6. In a circuit interrupter, a plurality of stationary contact members, a plurality of movable switch members cooperating therewith for opening and closing a plurality of poles, said stationary contact members and said movable switch members having engaging contact faces, some of said movable switch members being mechanically tied together by a tie means, an operating mechanism connected to said tie means for moving all of said mechanically tied together switch members to the open and closed positions, means biasing said engaging contact faces toward each other with a predetermined normal force, and magnetic means associated with some of said switch members for supplying an additional force biasing some of said engaging contact faces toward each other.

7 In a circuit interrupter, two stationar contact members and two movable switc members, said stationary contact members and said switch members having engaging contact faces, a tie means for mechanically connecting said switch members, a single operating mechanism actuating both of said switch members through said tie means, means biasing said engaging contact faces toward each other with a predetermined normal force, and means of magnetic material for. supplying an additonal force biasing at least i one pair of said engaging contact faces toward each other.

8. In a circuit interru ter, a stationary contact member, a pivotal y mounted switch member for cooperatin therewith to open and close the circuit, said pivotally mounted switch member having a contact member pivotally mounted thereon for engaging said stationary contact member, and magnetic means biasing said pivotally mounted switch member and said pivotally mounted contact member about their respective pivots.

9. In a circuit interrupter, a base member, a stationary contact member mounted thereon, a movable switch member cooperating with said stationary contact member to open and close the circuit, said movable switch member having a pivotally mounted contact member for engaging said stationary Contact member, and magnetic means for biasing said engaging contact members toward each other, said magnetic biasing means including means of magnetic material forming a part. of said movable switch member, and means of magnetic material supported upon said base member for attracting said means of magnetic material forming a part of said movable switch member.

10. In a circuit interrupter, a base member, a stationary contact member mounted thereon, a pivotally mounted switch member cooperating with said stationary contact member to open and close the circuit, said pivotally mounted switch member including a frame member having a portion of magnetic material and a pivotally mounted contact member, said stationary contact member and said pivotally mounted contact member having engaging contact faces, and magnetic means for biasing said engaging contact faces toward each other, said magnetic means including a member of magnetic material supported upon said base member for attracting said portion of magnetic material of said frame member, said attraction biasing said .switch member and said pivotally mounted contact members about their respective pivots.

11. In a circuit interrupter, a plurality of stationary contact members and a plurality of movable switch members cooperating therewith for opening and closing a plurality of poles, said stationary contact members and said movable switch members having engaging contact faces, said movable switch members being mechanically tied together by a bar tie, an operating mechanism connected to said bar tie, at a point intermediate the ends thereof, for moving all of the switch members to the open and closed positions,

means biasin said engaging contact faces toward each ot er with a predetermined normal force, and magnetic means associated with some of said switch members adjacent the ends of said bar tie for supplying an additional force biasing their engaging contact faces toward each other.

12. In a circuit interrupter, a base member, a plurality of stationary contact members, a plurallty of movable switch members cooperating therewith for opening and closing a plurality ofl poles, said switch members having a frame member, a portion of which is of magnetic material, and a contact member pivotally mounted thereon, said stationary cont-act members and said pivotally mounted contact members having engaging contact faces, said movable switch members being mechanically tied together by a bar tie aiiixed to each of said frame members, an operating mechanism mechanically connected to said bar tie, at a point intermediate the ends thereof, for simultaneously moving all of the switch members to the open and closed position, means biasing said engaging contact faces toward each other with a predetermined. normal force, and magnetic means for supplying an additional force biasing some of said engaging contact faces toward each other, said magnetic means including members of magnetic material aiixed to said base member for attracting said portions of magnetic material of said switch member frames.

13. In a circuit interrupter, a base member, a plurality of stationary contact members, a plurality of movable switch members cooperating therewith for opening and closing a plurality of poles, said switch members having a channel shaped frame member, a portion of which is of magnetic material, a contact member pivotally mounted thereon, and a conducting shunt affixed to said pivotally mounted contact member, said stationary contact members and said pivotally mounted Contact0 members having engaging contact faces, said movable switch members being mechanically tied together by a bar tie affixed to each of said frame members, an operating mechanism mechanically connected to said bar tie, at a point intermediate the ends thereof, for simultaneously moving all of the switch members to the open and closed position, means biasing said engaging contact faces toward each other with a predetermined normal force, and means of magnetic material supported by said base member, and energized by the current flow through said intcrrupter for attracting the portion of magnetic material of each of said switch member frames, each of said conducting shunts having a portion which extends along the portion of magnetic material of said frames and which is magnetically attracted thereto, the attraction between said shunts and said frame portions biasing each of said pivotally mounted contact members toward the engaging stationary contact member.

BENJAMIN I). BAKER. MAURICE W. BRAINARD. 

